1. Field of the Invention
The present invention relates to a semiconductor device and a method for manufacturing the semiconductor device, more particularly, a semiconductor device in which decrease of breakdown voltage property is suppressed and response speed is improved, as well as a method for manufacturing such a semiconductor device.
2. Description of the Background Art
In recent years, in order to achieve high breakdown voltage, low loss, and the like in a semiconductor device, silicon carbide has been adopted as a material for a semiconductor device. Silicon carbide is a wide band gap semiconductor having a band gap larger than that of silicon, which has been conventionally widely used as a material for semiconductor devices. Hence, by adopting silicon carbide as a material for a semiconductor device, the semiconductor device can have a high breakdown voltage, reduced on-resistance, and the like.
An exemplary semiconductor device adopting silicon carbide as its material is a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) or the like. The MOSFET is a semiconductor device that controls existence/non-existence of an inversion layer in a channel region in accordance with a predetermined threshold voltage so as to conduct and interrupt a current. For example, a trench gate type MOSFET or the like has been considered. A feature of the trench gate type MOSFET lies in formation of the channel region along a wall surface of the trench (for example, see Japanese Patent Laying-Open No. 9-74193 (Patent Literature 1)). In the trench gate type MOSFET, on-resistance can be reduced, but breakdown voltage property is disadvantageously decreased due to electric field concentration in the bottom portion of the trench. To address this, for example, there is proposed a MOSFET or the like having a trench in which a source electrode is disposed, apart from the trench in which the gate electrode is disposed (for example, see Y. Nakano, R. Nakamura, H. Sakairi, S. Mitani, T. Nakamura, “690V, 1.00 mΩcm2 4H—SiC Double-Trench MOSFETs”, International Conference on Silicon Carbide and Related Materials Abstract Book, (United States), Sep. 11, 2011, p. 147 (Non-Patent Literature 1)).
In the MOSFET proposed in Patent Literature 1, the source electrode is in contact with a source region, and is connected to a body region via a contact region adjacent to the source region. Accordingly, for example, when switching the operating state of the MOSFET (from ON state to OFF state), injection of holes from the source electrode to the body region is hindered due to an influence of a depletion layer extending from a pn junction between the source region and the contact region. This results in decreased response speed of the MOSFET, disadvantageously.
In the MOSFET proposed in Non-Patent Literature 1, a contact surface between the source electrode and the substrate is formed close to the drain electrode relative to the bottom surface of the trench. Accordingly, a metal composing the source electrode is readily diffused into the drift region, whereby stacking faults extend from the contact surface to the drift region. As a result, the breakdown voltage property of the MOSFET is decreased, disadvantageously.